1. Technical Field
The present invention relates to semiconductor devices and fabrication, and more particularly to methods and devices for separating monolayers in a layer of graphene using a stressor layer.
2. Description of the Related Art
Microelectronics applications have been increasingly employing graphene devices due to their conductive, mechanical and other properties. Processing of graphene is often unconventional relative to traditional processing techniques and is often difficult to control and incorporate into semiconductor processing. Graphene may be obtained using many techniques. One popular technique includes micro-mechanical alleviation of graphite. This includes employing adhesive tape to repeatedly split graphite crystals into increasingly thinner pieces. The tape with attached optically transparent flakes is dissolved in acetone, and the flakes including monolayers were sedimented on a silicon wafer. This has been improved by dry deposition, avoiding the stage when graphene floated in a liquid. This is often referred to as a “scotch tape” or drawing method. This technique may not produce a uniform graphene film.
Another method of obtaining graphene is to heat silicon carbide (SiC) to high temperatures (>1,100° C.) under low pressures (˜10−6 Torr) to reduce it to graphene. This process produces epitaxial graphene with dimensions dependent upon the size of the SiC substrate (wafer). The face of the SiC used for graphene formation, silicon- or carbon-terminated, highly influences the thickness, mobility and carrier density of the graphene. Exfoliation and transfer of the graphene layer is often very difficult.
Another method uses the atomic structure of a metal substrate to seed the growth of the graphene (epitaxial growth). In one technique, copper foil is employed, and, at very low pressure, the growth of graphene automatically stops after a single graphene layer forms. Arbitrarily large graphene films may also be created by chemical vapor deposition (CVD) growth. Multilayer graphene will also form on copper. However, exfoliation and transfer of the graphene layer is very difficult. Another disadvantage of CVD growth on metal substrates is that the grown graphene layer is a poly-crystal.